The condition of frailty is gaining international attention as the population of older adults rises globally. Frailty is characterised by a decline in functioning across multiple physiological systems, accompanied by an increased vulnerability to stressors.1, 2 It is associated with increased mortality, hospitalisation, falls, and admission to long-term care.1, 2 There is also much individual burden for a person living with frailty, including impaired quality of life and loneliness.3, 4
The concept of frailty is constantly evolving in the literature, and there is a progressive debate about how to define the condition.5 This debate aside, three important factors have remained consistent over the past decades in the conceptualisation of frailty.6 First, frailty is multidimensional, with physical and psychosocial factors playing a part in its development. Second, although its prevalence does increase with age, frailty is an extreme consequence of the normal ageing process. Third, frailty is dynamic, which means that an individual can fluctuate between states of severity of frailty.6
Frailty is potentially preventable, up to a probable point of no return when it becomes a pre-death phase. Therefore, strategies to prevent and slow the progression of frailty are paramount.7 To identify which people would benefit from such strategies, an expansive body of research has been devoted to developing tools to objectively quantify frailty, with persisting disagreements about the conceptual framework to be measured. In 2001, Fried and colleagues described the clinical presentation of frailty in terms of a physical phenotype, the clinical presentation of a definable biological syndrome.1 According to this frailty phenotype, an older adult is diagnosable with frailty if they score positive for three or more symptoms or signs out of five criteria. Also in 2001, Rockwood and Mitnitski introduced their frailty index, which is based on an accumulation of age-related deficits.8, 9 In their model, frailty is a continuous score summing signs, symptoms, disabilities, and diseases. The characteristics of these two concepts, which currently dominate the field, are listed in panel 1. Although the concepts differ, there is some common ground, as shown by overlap in determinants and identification of frailty.2
Key messages
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The condition of frailty is associated with adverse outcomes and increased health-care costs
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Frailty occurs in adults at any age, but it is more prevalent in older adults
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The global impact of frailty is expected to increase due to population ageing, particularly in low-income and middle-income countries
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Risk factors for the onset of frailty span across a wide range of sociodemographic, clinical, lifestyle-related, and biological factors
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Considering the degree of frailty of a person in clinical practice could result in more patient-centred care and avoidance of harm in primary, secondary, and tertiary prevention of disease
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Although the concept of frailty is increasingly being used in primary, acute, and specialist care, the translation from research to clinical practice remains a challenge for the coming years; specificity and standardisation of frailty measures is essential for progress
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Longitudinal research on trends and trajectories is a high priority for the frailty research agenda, as well as randomised controlled trials focused on prevention or treatment of frailty
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Using a life-course approach might increase our understanding of how frailty and its risk factors develop in earlier life stages, and could contribute to the development of public health strategies for frailty prevention
There is also controversy over whether frailty should encompass functional limitations, or whether it should be viewed as a pre-disability state. In addition, increased attention has been given to frailty subtypes, such as social frailty, nutritional frailty, and cognitive frailty.11 However, evidence for these subtypes is still limited. Another construct that has recently been proposed is the concept of intrinsic capacity, which emphasises the physical and mental capacities of an individual, instead of an approach focused on losses as captured by traditional frailty measures.12 The concept is endorsed by WHO but has not been empirically validated.
This is the first of a two paper Series on frailty, based on the latest evidence. In this paper, we describe the implications of frailty for clinical practice and public health. We will focus on frailty in older adults, but frailty can occur in adults at any age—especially in those with chronic illnesses. We provide an overview of the global impact and burden of frailty, including that in low-income and middle-income countries (LMICs), the usefulness of the frailty concept in daily practice, potential targets for frailty prevention, the importance of taking a life-course perspective, and the directions that need to be explored in the future. The description of preclinical models will not be covered in the present paper. The management of frailty, including interventions, is presented in the second paper.